Theoretical approach to study the formation of C2H4O2 isomers in interstellar medium through reaction between interstellar formaldehyde molecules*

The three isomers of C2H4O2, viz., glycolaldehyde (HCOCH2OH), acetic acid (CH3COOH) and methyl formate (HCOOCH3), have been detected in copious amounts in the interstellar medium (ISM). The possibility for formation of these molecules through interstellar formaldehyde (HCHO) has been explored by using the quantum chemical approach described by density functional theory (DFT) and second order Moller-Plesset perturbation (MP2) theory with a 6-311G(d,p) basis set in the gas phase as well as in icy grains. The associated molecule-molecule interactions have been discussed to study the formation of isomers of C2H4O2 in ISM. The reactions of two formaldehyde molecules exhibit a considerable potential barrier but due to quantum tunneling, these reactions could be possible in ISM. The chemical pathway is exothermic, which gives rise to a high probability for the formation of all three isomers, viz. glycolaldehyde, methyl formate and acetic acid, in interstellar space. Anharmonic rotational vibration, centrifugal distortion constants and coupling constants are also calculated and results suggest that the vibrations are harmonic in nature.